Much has been made of their fairness, subject matter, and even their biases, but no one can argue over their importance. Perhaps there will be a day when they are part of the annals of academic history, but for now, the ACT and SAT are critical to college admissions.
For a long time, the ACT was simply taken by students in the midwest, but in recent years, it's caught up with the SAT in terms of popularity nationwide. ACT scores range from from 1-36, and there are five components, Reading Comprehension, Mathematics, Science Reasoning, and Writing. However, the writing component is not a requirment. Each component is an individual test.
By contrast, the SAT, has only three sections, math, critical reading, and writing. Here, the scores range all the way from 600-2400. Yes, as was famously pointed out in the movie Blue Chips, you get hundreds of points just for signing your name correctly. Unlike the ACT, each SAT component is made up of multiple sections . The critical reading and math sections are three tests each. The writing section, which unlike the ACT is a requirement, is just one section.
Sometimes I hear students as if they should take the ACT or SAT. I hope they are getting the advice that they should take both.
There are absolutely related skills on these tests, but they are far from identical. You might score much higher on one than other. Think about the fact that the critical reading tests on the SAT emphasize vocabulary and the reading comprehension test on the ACT really doesn't. Depending on whether you are strong with vocabulary or not, that could make a huge difference.
It is true that there could be reasons to choose to just take one of the tests. If you are trying to avoid taking a writing test, then you'll definitely choose the ACT. On the other hand, if mathematics is a strength of yours, the SAT could be an advantage because that score counts for one third of your total instead of one fourth (or fifth if you take the writing) of the total ACT score.
Even though I'd advise you to take both, if you choose to only take one, it would still be smart to invest time preparing for the test. Try to get some practice, especially math ACT or SAT practice. The closer you get to test time, the more you should try to let go of your anxiety. This is your chance to impress the college or university of your choice with all you've learned over all your years of schooling.